One of the difficult and expensive problems in rail-roading is that of removing coal from open gondola rail cars to which the coal is frozen.
Present practice is to bake trains of cars in sheds for several hours to thaw the entire contents enough for removal. Heating to the temperatures necessary and for the length of time necessary in this method sometimes ignites the upper layer of coal. The fixed facilities and energy and the time required make this a very expensive system, and one that has some danger associated with it because of potential fume and fire hazards.